A very common building structure is based on wood-framing connection using framing members tied to the foundation or roof, and framing members attached to other framing members with fasteners. Recently, building codes recommend reinforcement of building structures using metal ties or metal straps between the framing member and the roof structure. While this building practice has performed well, damage to building structures due to high energy stresses such as hurricanes, tornados and earthquakes is a constant unmitigated occurrence.
It is evident that significant problems exist in building constructions located in coastal areas and in tornado prone areas. There is a need for reinforcement materials and techniques that reinforce new and existing structures while providing safety for building occupants. Surveys show that a significant portion of the damage resulting from hurricanes and earthquakes occurs in the connection between the roof and the wall of the building due to excessive deformation and movement of structures. In particular, the connection between the roof rafter or truss and the top plate is critical for the uplift force applied by high-wind events such as hurricanes. To increase the uplift capacity of rafter to top plate connections, building code provisions describe reinforcing them by using methods including toe nailing, metal straps and adhesives such as epoxies. Surveys also indicate problems with practices used to tie and strengthen framing members to the foundation or roof, and framing member to framing member. For example improper connections are made between the walls and the roof including but not limited to improper toenailing the rafter to the top plate. Missing or improper attachment of metal straps such as hurricane ties, are further examples of poor construction practices resulting in significant damage of the roof to wall connection and the sill-band joist-sole plate connection. Therefore, there is a need for a simple and improved construction method to reinforce conventional building structures. A desirable construction method should increase the strength and reduce the deformation of wood structures to restrict or eliminate the damage of framing member connections.
In the past, reinforcement methods have been applied to wood structures that include coatings and adhesives. Reinforcement of wood member joints has been achieved using a variety of connecting means including metal straps and epoxy adhesives. U.S. Pat. No. 5,501,054 to Soltis discloses a multi-layer fiber reinforcing material and an epoxy resin coating to reinforce wood members. However, the application of the adhesive and fiber directly to wood member joints during the building construction or by retrofitting an existing structure by adding wooden blocks to the wood connection is an expensive and difficult process.
A common problem in the application of coatings to wood structures is the rather small increase in wind uplift capacity such as dosed-cell polyurethane foam to avoid framing member deformation or even failure. US published Pat. Appl. No. 2008/0313985 to Duncan provides a method for increasing the wind uplift resistance of wood-framed roofs and side-wall structures using closed-cell polyurethane foam. An increase of uplift capacity is obtained by applying a 3 inch or more thickness of polyurethane foam covering the entire roof sheathing and side walls. The polyurethane foam produced a rather moderate increase in wind uplift capacity. It is also known to the artisan in the art that polyurethane generally exhibits an inferior elongation before failure, and also an inferior heat stability compared to most polyurea resins. Thus, often complex multi-layer resins and composites and textile and/or fiber embedded resins are needed to achieve building structures that show an increase in energy absorption capacity. For example, U.S. Pat. No. 8,087,210 to Agneloni discloses applying several layers of elastic materials and additional fiber containing material film to a building structure to achieve some reinforcement. Typical Polyurea that is commercially available typically has a tensile strength range between 8.3 MPa and 45 MPa, and an elongation at break between 100% and 1000%.
It would be desirable to develop a reinforcement method containing a field or factory applied elastomer without any fiber reinforcement materials for improving the wind load-bearing capacity and deformation energy of wood member joints of a building structure.